The long-term goal of this research is to discover the structural features of sensory neurons that define their capacities to code Information. The emphasis Is on the cytological design and pattern of connections of specific types of auditory neurons and their synaptic contacts at the levels of the cochlear nucleus, superior olive, and cochlea. The specific aims are to define the synaptic organization of certain types of neurons In the cochlear nucleus that Initiate the ascending monaural and binaural pathways. to define their connections with other neuronal types In the cochlea and superior olive, Including their Inhibitory and excitatory synapses, and to relate these findings to the circuits responsible for binaural processing. The key morphological concept In this effort Is the synaptic profile, which quantitates the concentration of the different kinds of synaptic endings on each part of a cell. The hypothesis Is that each population of neurons defined In this way will differ with respect to one or more other features, morphological, neurochemical, and electrophysiological. The synaptic profile provides a map on which to plot the locations of the endings with respect to their origins from other nuclei or neuronal types and the neurotransmitters contained In the endings, and for quantitative comparisons between the results of different kinds of experiments. Light and electron microscopic methods are used. Sufficient details are obtained to correlate with physiological recordings from these neuron types in related studies. Anterograde or retrograde labeling of neurons with cellular tracers will be combined with immunocytochemical labeling methods to define the connections of specific types of neurons and to show which of these are associated with the known Inhibitory transmitters. This will provide a cellular basis for pursuing an understanding of the normal and abnormal function of the central auditory system, and ultimately a biological basis for neurochemical or prosthetic therapies of nerve deafness.